The Housing Industry Today
The present residential construction industry can be divided into segments based on the three basic methods which are utilized to produce dwellings: manufactured or modular (manufactured), panelized or component (panelized)--with elements fabricated both on and off site, and individually built (stick-built)--with dwelling construction in-place at a specific building site. Each of these three methods have distinct advantages and disadvantages. In addition, each method is suited to produce a particular type of dwelling. A common goal of the residential construction industry is to produce quality dwellings that have broad market appeal in a cost efficient manner.
The manufactured home is built in a factory which is geographically remote from a housing development or a particular building site. The factory produced modules must be transported over public highways and roadways to a dealership or predetermined building site. The earliest of this class of homes were called mobile homes. They were, and still are, equipped with axles attached to an undercarriage framework. The typical manufactured home is built in a factory which serves a broad geographic region, ranging in size from tens or hundreds of miles in radius to several states. Because of the cost efficiencies inherent in factory production, the manufactured (and some panelized) method is successful in producing lower cost new housing typically for small size homes. A manufactured home is produced for direct sale to a customer and installation at a particular building site or it may be sold to a dealer and held in inventory for a subsequent sale and installation.
The present day manufactured home offers significant improvements over the former mobile home. A plurality of manufactured modular segments may comprise the finished home and the modules are transported from a remote factory to a dealership or destination building site. Once delivered to the final building location, the modules are joined together to form a resultant dwelling that is significantly larger than a typical 12''.times.70' single module manufactured home.
The major advantage of manufactured homes is the use of a factory environment. Within a factory setting, a controlled environment exists where complete, roadable dwellings are built. Factories represent a significant advantage in mass production efficiency. The advantages of a factory environment are:
Dwellings can be produced very quickly from order to finished product. PA1 Foul weather has negligible impact on production. PA1 Construction tolerances are more precise and more controllable. PA1 Increased production through multiple shifts is readily achievable because the critical conditions of lighting, ventilation and air temperatures are controlled 24 hours a day. PA1 Non-sequential construction techniques are possible. PA1 A Federal (HUD) Building Code can be utilized which offers a streamlined regulatory environment since it is focused on performance standards rather than implementation standards. In addition, homes built to the HUD Building Code are less expensive to produce than stick-built homes which are built to the Uniform Building Code (UBC) or other local building codes. PA1 Major cost efficiencies are realized in both the quantity of labor hours necessary to build homes, and the unit cost for labor because of the use of repetitive production tasks and the ability to bulk purchase and handle materials at a fixed manufacturing location. PA1 Pre-fabricated panels for production of homes in "remote" regions can be accomplished. PA1 Ability to build a wide diversity of standard size dwellings (including single and multi-story). PA1 Individual customization is easy. PA1 Well known and widely accepted method of construction. PA1 Skilled subcontractors are generally available. PA1 Dimensional and design constraints have confined manufactured homes to a limited market segment. PA1 The manufactured method cannot be used to build standard size homes without segmentation of the home into modules of relatively small dimensions which results in design and floor plan compromises. PA1 The manufactured modules must be transported a significant distance from the factory to the building site, often via a dealership. PA1 Manufactured home segments are subject to significant architectural and floor plan constraints because of the need to transport the completed modules over public highways and roadways. PA1 There are significant size limitations in manufactured homes: single-story, 10-14 ft wide by 50-70 ft long with box-like architecture. PA1 The cost of field mating the roadable manufactured modules and related field quality control necessary for assembly and finishing can be significant. PA1 There is a possibility for damage to manufactured home modules during extended transport over the public highway system. PA1 Field labor is required for field assembly of panels. PA1 Less than complete dwelling units are produced, since it is a method to produce only segments of homes. PA1 The panelized method of construction cannot build standard size homes without segmentation of the home into modules of relatively small dimensions which results in many compromises. PA1 The panels or components that are manufactured require major field assembly which takes a significant amount of time and are therefore exposed to local weather conditions. PA1 The panels built in a remote plant have size limitations because of the necessity to transport these panels over public highways and roadways. PA1 The panels must be assembled at the project site, and construction joints between the panels must be repaired and finished at the project site. PA1 Major design constraints exist because panels must be roadable. PA1 There is a possibility for damage to panels and components during extended transport and handling. PA1 Stick-built construction is inherently a sequential home building process floors are built before walls, walls before ceilings and the roof after all the other framing is completed. This is a lengthy process and therefore results in construction activity of extended duration. PA1 Much of the work done in stick-building a dwelling is at the mercy of local weather conditions which can delay schedules and damage materials. PA1 Bulk material delivery and handling are not possible because the materials need to be segregated for each individual home. PA1 The materials and supplies are mostly hand carried, piece-by-piece, into and within the house during construction. PA1 It is common to have 4 to 10 month construction schedules in stick-built construction of a dwelling. PA1 Homes must conform to the local building codes, such as the Uniform Building Code (UBC), without any ability to build to the Federal (HUD) Building Code which would be faster, less expensive, and provide an easier regulatory environment. PA1 The cost of labor in stick-building is high to thereby attract the necessary skill levels to widely scattered job sites. PA1 Supervision and quality control in stick-building is non-uniform.
A method of dwelling construction which has similarities to the manufactured dwelling technology is the panelized method of construction. Panelized construction consists of a system for prefabricating walls, floors and roof components into units or sections. This method of construction is most efficient where there is a repetition of the panel types and dimensions. Panels are manufactured using a jig, into which the framing members are placed and then interconnected via nails, screws or welds. The interior and exterior sheathing, or even the complete interior or exterior finish, may be applied to the wall panel prior to the finished panel being hoisted onto the structure. Shop panelization offers numerous advantages. The panel shop provides a controlled environment where work proceeds regardless of weather conditions. The application of sheathing and finish work is easier and faster with the panels placed in a horizontal position instead of a vertical position.
With panelized construction, major components of homes are either prefabricated in a remote factory environment or at the site where, unfortunately, panel fabrication is exposed to local weather conditions. If components or panels are built in a factory, they are subsequently transported over public highways and roadways to the building site where they are hoisted into place and interconnected to form the basic dwelling structure using conventional building techniques. The panelized construction technique requires the use of hoisting equipment at the building site to handle the preassembled components and also requires that significant amounts of finish work be performed at the site to assemble components and finish construction joints between panels.
The major advantages of panelized construction are the following:
Cost and production efficiencies of off-site factory panel fabrication. PA2 Efficiencies of mass producing panels at a project location can also be realized. PA2 Assembly of panels or components into finished homes is reasonably fast.
The remaining category of residential housing is the stick-built house that is either custom built according to an owner's individual specifications, or as a builder's spec home, or constructed as one of a plurality of pre-existing models in a housing development. These dwellings are built in the traditional manner of using framing members (typically dimensional lumber) to fabricate the dwelling on a foundation at the building site according to a set of architectural plans. Stick-built home design differs greatly from manufactured home design. There are no architectural, structural or dimensional limitations with stick-built housing like those imposed on manufactured design by virtue of the roadway transportation limitations. Transportation over public roads involves height, width, length and weight restrictions. In stick-built construction, height, width, depth, roof pitch, roof overhang, gabled, dormered, etc. are all completely open to individual tastes limited only by the governing building code restrictions. The ability to produce standard size homes with substantial design flexibility is the reason that the majority of homes built today are stick-built homes.
Stick-built construction requires a sequenced building format, where item A must be completed before item B can begin, and in turn, item B must then be completed before item C can begin and so on. For example, the ground level walls must be completed before the second level floor can begin, and the second level walls must be completed before the second level ceiling can begin. While this method of residential home construction has worked for many years, there are inherent inefficiencies in this method that result in significant cost penalties to the home buyer.
Stick built dwellings can be built to any size or layout that is desired within the limitations of the structural capabilities of the framing material. Multi-story homes can easily be built with the architectural features, room size and layout being determined by the architect, home builder and/or owner. There are no overriding constraints imposed by a need to transport the structure over the existing public highway or roadway system. Other advantages of stick-built construction techniques are:
Thus, it is evident that each of the above-noted methods of residential dwelling construction have certain distinct advantages, which advantages are typically intimately coupled with the type of dwelling produced by the selected method of construction.